Stem cells turned into sperm

They've got to be the youngest fathers yet. Stem cells taken from mouse embryos have been used to generate sperm that went on to fertilise eggs and produce live offspring. The technique could one day help an infertile man to have his own biological children.

Sperm have been created from stem cells and injected into eggs before, but the resultant embryos stopped growing after a couple of days. "We think it's a big step forward," says Karim Nayernia at the University of Newcastle upon Tyne, UK, a member of the team that carried out the research.

Stem cells were extracted from early mouse embryos, and coaxed into becoming sperm by manipulating the environment in which they were grown in the lab. These sperm were then injected into normal mouse egg cells to fertilise them (Developmental Cell, DOI: 10.1016/j.devcel.2006.05.010). Of 65 embryos implanted, seven mouse pups were born, six of which survived to adulthood.

Problems with the procedure remain, however. The six mice that survived were all abnormally large or abnormally small, and were infertile. Many developed lung tumours and none lived for more than five months - well short of the typical three-year mouse lifespan. Also, the sperm themselves had shortened tails and were unable to penetrate eggs on their own.

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